/Engine/Source/Runtime/Engine/Public/MaterialShared.h
Gather anyUMaterialExpressionCustomOutputexpressions in the material and referenced function calls
virtual void GatherExpressionsForCustomInterpolators ( [TArray](API\Runtime\Core\Containers\TArray)< class [UMaterialExpression](API\Runtime\Engine\Materials\UMaterialExpression) * > & OutExpressions ) const